1. Field of the Invention
The present invention relates generally to a water heater, and more particularly to a method for controlling water temperature of outlet water of a water heater and the controlling device thereof.
2. Description of the Related Art
FIG. 1 shows a conventional water heater 500 capable of controlling water temperature. The water heater 500 includes a water pipe 510, a gas pipe 520, and a temperature controller 530. The water pipe 510 has an inlet 511 and an outlet 512. The temperature controller 530 includes a gas controller 531, a burner 532, a temperature sensor 533, and an operational controller 534.
The gas pipe 520 provides gas to the burner 532 that the burner 532 may heat water in the water pipe 510. The gas controller 531 is provided at the gas pipe 520 to adjust a flow rate of gas to the burner 532. The temperature sensor 533 is provided at the outlet 512 of the water pipe 510 to sense an outlet water temperature of the heated water. The sensed temperature is sent to the operational controller 534 that the operational controller 534 may control the gas controller 531 according to the temperature.
A user may set a desired temperature that the operational controller 534 may control the gas controller 531 according to the difference between the outlet water temperature and the desired temperature. The operational controller 534 controls the gas controller 531 to provide more gas when the outlet water temperature is lower than the desired temperature, and the operational controller 534 controls the gas controller 531 to provide less gas when the outlet water temperature is higher than the desired temperature to maintain the desired temperature.
However, such water control method still has the following drawbacks:
As shown in FIG. 2, when the conventional water heater 500 is heating water, the outlet water temperature is lower than the desired temperature at time (a) that the operational controller 534 controls the gas controller 531 to provide the burner 532 more gas to keep the temperature rising. At time (b), the sensed temperature is equal to the desired temperature that the operational controller 534 controls the gas controller 531 to provide the burner 532 less gas. However, the water has been heated before time (b) that the outlet water temperature keeps rising. The outlet water temperature is much higher than the desired temperature at time (c) that the gas controller 531 provides less gas and the operational controller 534 keeps controlling the gas controller 531 to provide lesser gas to drop the temperature. The gas controller 531 is instructed to provide more gas again after time (d), which the outlet water temperature is equal to the desired temperature, but the temperature keeps dropping until time (e). After that the water temperature is kept being adjusted around the desired temperature and becomes steady gradually. In conclusion, the conventional water heater 500 is not an optimum device and needs to be improved.